Efficacy and Mycobactericidal Action of Aldehydes: Structure-Activity Relationship

Abstract

The aliphatic di-aldehyde glutaraldehyde (GTA) and the aromatic di-aldehyde ortho-phthalaldehyde (OPA) are used for the high-level disinfection of medical devices because of their broad spectrum microbicidal efficacy. Mycobacteria represent a particular challenge to disinfection as they are intrinsically resistant organisms to many microbicides. Indeed some Mycobacterium chelonae strains isolated from endoscope washer-disinfectors have been shown to be resistant to in-use concentrations of GTA, although they remained susceptible to OPA. Although OPA is a more potent microbicide, it is only beginning to become understood as to the reasons why. Studying the interactions of the di-aldehydes at the molecular level, for example with amino-acids, but also at the cellular level, with whole cell micro-organisms, has provided an understanding as to the difference in mycobactericidal activity between the aliphatic and the aromatic di-aldehydes. Notably, an understanding of their reactivity, lipophilicity, cross-linking ability, and penetration mechanism provides an altogether solid explanation for the enhanced efficacy of OPA. Although knowledge of molecular and macro-molecular interactions of a microbicide is important, the study of its interaction with whole cell organisms is necessary to explain overall microbicidal efficacy. This chapter provides an example of such an understanding by reviewing and interpreting the study of di-aldehyde interactions with mycobacteria performed in this laboratory and others.